The aim of the invention is to control the operation of a bulk good grate cooler to cool heated bulk goods such as cement clinkers that are transported from the bulk good inlet connection via suitable conveyors to the chilled goods discharge connection, while the cooling grid and the hot bulk goods distributed onto the grid are supplied with cooling air flow passed from the bottom up, which is regulated by control systems arranged beneath the cooling grid.
In a cement clinker production line, the hot cement clinker produced from calcinated raw meal by a rotary kiln is dropped from the discharge point of the kiln onto a cooling unit, usually onto the cooling grate of a grate cooler, onto which the clinker is distributed and transported by suitable conveyors in longitudinal direction to the cooler discharge point. During this process the cooling grate and the hot bulk material layer are essentially ventilated from bottom up by cooling air. In the following, some of the more well-known grate cooler types shall be briefly illustrated.
In the case of a reciprocating grate cooler, fixed grate plate sequences and reciprocal grate plate sequences alternate in the course of conveyance, all grate plates are furnished with cooling air vents and are essentially ventilated from bottom up by cooling air. By the joint oscillating movement of all movable grate plate sequences, the hot material to be cooled is transported batch-wise and cooled in the process.
An alternative to such reciprocating grate coolers is e.g. the grate cooler type EP-B-1 021 692 with which the cooling grate through which cooling air is passed is not movable, i.e. it is set. Numerous rows of adjoining reciprocal bar-shaped thrust elements are arranged above the cooling grate, which are moved between the pre-stroke position in the cooling material conveyance direction and the return stroke position, so that the reciprocating movement of these elements within the cooling bed successively move and cool the material from the cooler start point to its end point.
Irregular distribution in the hot bulk material bed in terms of height of bulk material bed, clinker grit size, temperature profile, etc. cannot always be avoided with these types of grate coolers, which in turn also causes irregular cooling. In cooling grate areas with a larger bulk material bed height there is an increase in flow through-flow resistance for cooling air, a decrease in flow velocity and less cooling air is passed through the bulk material bed. In the opposite sense, a low bulk material bed height means a decrease in the through-flow resistance of cooling air and an increase in flow velocity and blowout risk. Too much cooling air is passed through such bulk material bed areas that would require the lowest amount of cooling air.
It is therefore known that when implementing a grate cooler to cool hot bulk goods such as cement clinker (EP-B-0 848 646) the specific cooling air quantity should be adjusted automatically in the cooling air flow beneath the cooling grid, so that in the case of an increasing cooling air flow quantity, caused by a decrease in cooling material bed height and flow resistance, the size of the cross section surface of the specific cooling air route is reduced, and conversely, in order to balance a changing decrease in pressure via the bulk material cooling bed in this manner, so that the specific cooling air quantity is no longer dependent on the respective pressure loss or flow resistance of the cooling air in the respective bulk goods bed zone. The well-known mechanical cooling air flow rate control system operates with a weight-loaded swing flap with a horizontal pivot axle, whereby the swing flap automatically restricts the cooling air inflow, the extent of which depends on the existing pressure and flow conditions. If the existing cooling air regulator, which operates with a purely gravitational operating lever weight with upstream flow body, were arranged below the cooling grid in the cooling air flow of the cooling grid zones, and were not fixed but rather, such as a reciprocating grate cooler for bulk goods transport with regulator, movable, the independent function of the regulator would be disrupted by the reciprocating movement, causing the regulating result to be falsified.
The above-mentioned independently operating cooling air control system of a grate cooler leads to the control of an essentially constant flow volume of cooling air. The common grate cooler control system does not take into account the individual cooling requirements in various zones of the, in practice, very long and wide grate cooler, which cannot optimally respond with a constant control of the cooling air volume flow. Need-driven changes of the cooling air volume flow within the individual zones of the grate cooler during operation are not possible with the common grate coolers.
With the EP-A-0 943 881 it is also known that the conveyor velocity of the grate cooler is regulated depending on the height of the cooling material bed as well as the cooling air flow resistance in the inlet area of the grate cooler. This leads to a homogenization of the cooling material bed. The so-called chamber pressure in the air chambers beneath the cooling grate is generally applied when measuring the flow resistance. As the cooling air chambers arranged successively in cooling direction are large, whereby the air chamber size at the end of the cooler generally increases, the measured chamber pressure, even in connection with the measured height of the bulk material bed, is no longer necessarily representative for the current cooling air requirements within one of the zones of the grate cooler.